Parallel strip transmission antenna array



Oct. 24, 1961 R. H. REED 3,

PARALLEL STRIP TRANSMISSION ANTENNA ARRAY Filed June 1, 1956 A TTORNE Y.

United States Patent j 3,005,986 PARALLEL STRIP TRANsMIssroN ANTENNAARRAY RichardH. Reed, Los Angeles, Calif., assignor to Hughes AircraftCompany, Culver City, Caiifi, a corporation of Delaware Filed June 1,1956, SenNo. 588,921 6 Claims. (Cl. 343-810) This invention relates toantenna arrays, and particularly to microwave antenna arrays which arelight, rugged and compact.

Antenna arrays for aircraft and other mobile installations usuallyshould be of minimum size and weight. Such arrays usually should conformto the streamlining of the airplane and, preferably, should be integralwith the aircraft structure. For these purposes, the arrays are usuallyassociated with a protective radome of the desired shape. Antenna arraysheretofore built have usually required that the components of the arrayprovide mechanical rigidity as Well as the desired electricalcharacteristics. Such construction usually substantially increases thesize and weight of the energy transmitting and radiating elements. Inaddition, further elements often are needed witirthis construction tosupport-the array from the ground plane. These factors have heretoforemeant that dipole arrays could not be employed, except in a fewlocations, without materially decreasing the streamlining of theinstallation in which they were employed. In particular, it hasheretofore been difiicult to arrange a light and compact streamlinedarray providing desired illumination from a central region of one of theplanar surfaces of an aircraft.

lt is therefore an object of this invention to provide an improvedantenna array which is characterized by ruggedness, simplicity ofconstruction, compactness and lightness in weight.

It is a further object of this invention to provide an improved dipolearray employing a smaller and lighter but at the same time strongermechanical arrangement than has heretofore been employed in the art.

Yet another object of this invention is to provide an improved microwavedipole array useful in a central region. of a planar surface, whicharray is extremely compact but at the same time is mechanically strongand also provides desired illumination characteristics.

An antenna array provided in accordance with this invention may bearranged around a plane-surface radome structure. The plane-surfaceradome may be sandwiched between and. supportthe strips of aparallel-strip transmission line. Radiation patterns may then beprovided from flat strip dipole elements extending from each of thestrips and, like the strips, sandwiching the radome. With thisconstruction, the transmission line and dipoles may be bonded to theradome, which may itself be honeycombed or otherwise apertured forweight reduction. Such -a structure is extremely light in weight becausethe electrical elements are fully supported by the radome and need nothave independent structural strength. Additionally, the structure isextremely compact because supporting stubs or other means for separatingfrom a ground plane are not necessary.

The novel features of this invention, as well as the invention itself,both as to its organization and method of operation, may best beunderstood when considered in the" light of the following description,when taken in connection with the accompanying drawing, in which likereference numerals refer to like parts, and in which:

FIG. 1 is a perspective view, partially broken away, of a linearmicrowave array in accordance with this in- 3,005,986 Patented Oct. 24,1961.

ice

vention which employs a central feed and a honeycomb radome;

FIG. 2 is a fragmentary View, partly broken away, showing detailedfeatures of the central feed system, the array and the honeycomb radomeof the arrangement of FIG. 1;

FIG. 3 is a fragmentary cross-sectional view of the arrangement of FIG.1, and

FIG. 4 is a simplified perspective view of an aircraft employing twoantenna arrays in accordance with the invention.

An arrangement for practicing the invention, referring now to FIG. 1,may employ a plate-like supporting structure 10 or panel of plasticmaterial. The supporting structure 10 may comprise a radome or otherstructural element for use on an aircraft. The structure 10 may describea flat or curved planar surface depending on the shape to which it is toconform or the arrangement of the array. The plastic employed may be anyone of a number of substances well known in the art which arenonconducting and substantially pervious to electromagnetic wave energy.The structure or panel 10 is preferably multiapertured, the aperturestransverse to the. plane of the structure it permitting decreased weightwhile retaining strength and rigidity. As shown, the apertures may be ina honeycomb pattern. It will be understood, however, that apertures neednot be employed and that the material need not even have a lowdielectric constant in some applications. Under particular conditions, asolid dielectric might be desired.

A linear antenna array 2! may be arranged on the supporting structure itin a central region of the surface of the structure 10. The linearantenna array 20' comprises a parallel strip transmission line 22including a pair of fiat elongated transmission strips 24. Thesetransmission strips .24- may be successively widened in step-wisefashion, and also varied in length to provide desired illuminationcharacteristics. The array 20 shown employs two successive steps 26 oneach end of the elongated strips 24 to provide a broadside array. Thebroad faces of the parallel strips 24 are placed against the supportingstructure 10 and on opposite side of the supporting structure 16. Thetwo strips 24 are parallel and coextensive with each other. Thethickness of the supporting structure 10 is dependent upon theseparation between the transmission strips 24, which in. turn isdependent upon the wave length of the energy transmitted. As shown inFIG. 1, supporting structure 10 almost fills the space between the twotransmission strips 24. For all practical microwave applications, thisprovides sufficient thickness to insure structural strength andmechanical rigidity.

Radiating elements 28 are coupled to and substantially normal to each ofthe parallel strips 24 and have their broad faces against the supportingstructure 10'. The radiating elements 28 are flat strip dipole elementsroughly corresponding in section to the transmission strips 24themselves. These radiating elements 28 are preferably made integralwith the transmission strips 24 but may be mechanically attached to thestrips 24. The radiating elements 28 are arranged in dipole pairs, withthe individual members of each pair being coupled to a differenttransmission strip 24 and thus being on opposite sides of the radomeit). The dipoles and transmission strips 24 provide a radiating arraywhich may be called a transmission line radiator.

The transmission line 22 is center fed by a coaxial line 3%} and acoupling probe 32. Transmission lines such as transmission line 22 may,however, be fed elsewhere than at their centers. The arrangement may beseen in more detail in FIGS. 2 and 3, to which figures reference is nowmade. The transmission lines 24 and the dipole members 28 aremechanically coupled to the supporting structure by suitablenonconductive bonding material 40, such as a glass cloth or otherplastic material well known in the art. The bonding material 40 does notdisturb the electrical characteristics of the system but does providefirm and positive attachment of the parts of the array to the supportingstructure 10. The bonding material 40 may be arranged as a sheet on thesupporting structure 10, with the transmission strips 24 and the dipolemembers 28 being sunk into the bonding material 40. Thus a flush,streamlined surface is provided.

A two-dimensional antenna array (not shown) may be provided by theemployment of a second linear antenna array spaced from the first on thesame radome, or placed on a second, adjacent radome. The elements of thesecond array can be like those of the first array and thus need notfurther be described.

In operation, electromagnetic wave energy fed by the coaxial line 30 tothe linear antenna array 20 energizes the system to provide the desiredillumination. It will be understood that any two-dimensionalillumination desired could be provided by a second linear antenna arrayin like manner. Energy transmitted along the transmission lines 24 fromthe center-feed coupling probe 32 will thus be radiated from the dipolemembers 28. Other desired illuminations can be obtained by adjustment ofthe characteristic impedance of the line formed by the parallel strips24.

It will now be apparent that the use of a plate-like supportingstructure 10 providing a radome function between associated transmissionstrips 24 and dipole members 28 bonded to the supporting structure it)provides many improvements over the prior art. A flush antenna array isprovided which may be arranged to conform to the outer surfaces of anairplane 50, as shown in FIG. 4. The array might be substantially flat,as shown on the tail surface of the airplane 50, or curved, as may beseen on the airplane 50 body. Further, the array might be spaced awayfrom the body or made flush with the body, as shown. In eitherarrangement the structure is thinner and more streamlined than thearrays of the prior art. A desired radiation pattern can be providedfrom any central region of a planar surface, although it will beapparent the device is not restricted to such use. The flat stripelements 28 which are used for dipoles and the transmission lines 24derive their strength from the supporting structure 10 and need haveonly minimum structural rigidity. This integral construction also, inefiect, eliminates the need for using spaced supporting stubs extendingfrom a separately disposed ground plane. Prior art dipole arrays havebeen restricted to a spacing of M4 Wavelengths between the array and theground plane, and have used supporting stubs of A/ 4 length. With thepresent array no such restrictions are imposed, and spacings of only A/8 have been successfully used.

Thus there has been described an improved antenna array. An integralconstruction may be used in which a supporting structure is sandwichedbetween the trans mission strips and dipole elements of an array. Bythis arrangement the size and weight of the antenna elements may beminimized and the stream-lining and compactness of the array improved.

What is claimed is:

1. A microwave antenna array comprising: a central, substantiallynonconductive, planar member having a plurality of transverse apertures;conductive strip members on each side of said planar member and spacedapart from each other, the broad faces of said strip members lyingsubstantially parallel to the plane of said planar member and said stripmembers each including transmission and radiating elements, said stripmembers together providing a radiating array; and sheets of bondingmaterial on each side of said planar member, coupling said strip membersto said planar member.

2. A microwave antenna array comprising: a substantially nonconductiveplaner structure having a plurality of transverse apertures defining ahoneycomb pattern; two conductive strip members, each adjacent adifferent side of said planar member and substantially parallel thereto,said strip members each including elongated portions parallel to eachother and defining a parallel stn'p transmission line, and alsoincluding radiating elements, each individual radiating elements of eachof said strip members being paired to an element of the other stripmember to form a dipole; two sheets of substantially nonconductivebonding material, each sheet lying between a different one of said stripmembers and said planar member and coupling them together; and means forfeeding wave energy to said transmission line.

3. A microwave antenna array comprising: a substantially nonconductivepanel having a plurality of transverse apertures; a transmission lineradiator in a central region of the surface of said panel and comprisingtwo flat strips each on a different side of said panel and having aplurality of radiating strips extending outwardly therefrom in the sameplane, each radiating strip being paired with and extending oppositelyfrom a radiation strip of the other parallel strip to form a dipoletherewith; and two sheets of nonconductive bonding material in the samecentral region of the surface of said panel, each sheet coupling adifferent one of said parallel strips to said panel and providing withsaid strip a flush outer surface for the assembly.

4. A microwave antenna array comprising: a multiapertured planarsupporting radome of a material pervious to wave energy; a parallelstrip transmission line, the individual ones of said parallel stripsbeing disposed on opposite sides of said radome and adjacent thereto; aplurality of strip dipole members coupled individually to the separateones of said parallel strips and lying adjacent said radome in the planeof the strips to which they are coupled, each dipole member of one ofthe parallel strips being paired with and extending oppositely from adipole member of the other one of the parallel strips to form a dipoletherewith; means including a layer of glass cloth for bonding saidparallel strip transmission line and said dipoles to said radome; andmeans including a coaxial line electrically coupled to said parallelstrip transmission line and mechanically coupled to said radome forfeeding said transmission line.

5. An improved antenna array which is characterized by lightness inweight, simplicity, and compactness, said array comprising: asubstantially flat radome having a plurality of apertures forming ahoneycomb pattern; a transmission line in a central region of thesurface of said radome and comprising coextensive parallel strips,having successively widened portions arranged to provide desiredillumination, With the individual ones of the strips being disposed onopposite sides of the radome and lying flat along said radome; aplurality of fiat strip dipole members integral with and extendingnormally from each individual strip of the transmission line, saiddipole members also lying fiat along said radome and being arranged indipole pairs consisting of a dipole member from each of said strips;bonding means including layers of glass cloth mechanically coupling saidparallel strips and said dipole members to said radome, said glass clothdefining a flush surface with said parallel strips and dipole members;and coaxial feed means centrally feeding said transmission line andmechanically coupled to said radome.

6. A dipole array comprising: a multiapertured planar radome member, aparallel strip transmission line coupled to said planar radome member,the strips of said transmission line being disposed on opposite sides ofsaid planar radome member, dipole elements comprising a plurality ofstrip members coupled individually to the strips of said transmissionline and disposed in the planes thereof and extending therefrom atspaced points therealong, and energy feed means coupled to said radomestructure anii electrically coupled to said transmission line at aselected point therealong for energizing the dipole elements With energytransmitted along the transmission line.

References Cited in the file of this patent UNIT ED STATES PATENTS 6Higgins et al. Aug. 5, 1947 Doerner Oct. 14, 1952 Havens July 7, 1953Arditi et a1. Dec. 11, 1956 Chu Dec. 29, 1959 FOREIGN PATENTS CanadaFeb. 15, 1955 Great Britain Aug. 1, 1951

